The present invention relates to an arrangement for cooling of recirculating exhaust gases of a combustion engine.
The technique called EGR (exhaust gas recirculation) is a known way of recirculating part of the exhaust gases in an exhaust line of a combustion engine. The exhaust gases are led through a return line and mixed with inlet air to the combustion engine before the mixture is led to the cylinders of the combustion engine. Adding exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used both for Otto engines and for diesel engines.
The amount of exhaust gases which can be supplied to a combustion engine depends on the pressure and temperature of the exhaust gases. Supplying as large an amount of exhaust gases to the combustion engine as possible entails effective cooling of the exhaust gases before they are led to the combustion engine. A known practice is to cool the recirculating exhaust gases in one or more EGR coolers before they are led to the combustion engine. The recirculating exhaust gases may in that case undergo a first step of cooling in an EGR cooler which is cooled by coolant from the combustion engine's cooling system and a second step of cooling in an EGR cooler which is cooled by coolant from a low-temperature cooling system. The exhaust gases may thus be cooled to a temperature close to the temperature of the surroundings.
During operation of the combustion engine, the exhaust gases will be at a temperature ranging from 150° C. to 600° C. The temperature of the recirculating exhaust gases will be highest when the combustion engine is under great load. In cases where the combustion engine's cooling system is used for cooling the recirculating exhaust gases, the cooling system will thus be subject to high load peaks at times when the combustion engine is under great load. In heavy vehicles, the combustion engine's cooling system is commonly also used for other cooling requirements in the vehicle, e.g. cooling the oil of a hydraulic retarder. It is therefore desirable to reduce the load on the combustion engine's cooling system.